Totally Aerated Combustion Burner

ABSTRACT

A totally aerated combustion burner is provided with a combustion plate part through which air-fuel mixture is ejected. The combustion plate part includes: a porous body made of metal fibers; and a distribution plate stacked on a back surface of the porous body, the distribution plate having formed therein a multitude of distribution holes, thereby enabling reduction in cost. The porous body is formed by nonwoven fabric made by laminating metal fibers in the form of felt. A front surface of the nonwoven fabric is covered by a meshed sheet made of metal. Preferably, the meshed sheet is made by knitting a wire member into the form of a mesh, the wire member being formed by bundling together a plurality of metal fibers. The mesh size of the meshed sheet shall preferably be below a flame-out distance of the air-fuel mixture to be ejected out of the combustion plate part.

BACKGROUND OF THE INVENTION 1. Technical Field

The present invention relates to a totally aerated combustion burner which is provided with a combustion plate part through which air-fuel mixture is ejected.

2. Related Art

In this kind of totally aerated combustion burner, there is known an arrangement in which the combustion plate part comprises: a porous body made of metal fibers; and a distribution plate stacked (overlapped) on a back surface of the porous body, the back surface being defined as an upstream-side surface of the porous body as seen in a direction of flow of the air-fuel mixture, and the distribution plate having formed therein a multitude of distribution holes. The air-fuel mixture can thus be ejected through the distribution holes and the porous body (see, for example, JP2014-9838A).

In the above-mentioned known example, the porous body is made up by knitting metal fibers into woven fabric. However, in order to knit this kind of woven fabric, metal fibers are required to be made extremely fine in preventing the knitting needle of a knitting machine from being mechanically broken. Since it costs a lot to manufacture this kind of ultrafine metal fibers, the example in the related art in which the porous body is made up of knitted woven fabric made of metal fibers becomes expensive.

SUMMARY Problems that the Invention is to Solve

In view of the above points, this invention has a problem of providing a low-cost totally aerated combustion burner which uses porous body made of metal fibers.

Means for Solving the Problems

In order to solve the above problem, this invention is a totally aerated combustion burner comprising a combustion plate part through which air-fuel mixture is ejected. The combustion plate part includes: a porous body made of metal fibers; and a distribution plate stacked on a back surface of the porous body, the back surface being defined as an upstream-side surface as seen in a direction of flow of the air-fuel mixture. The distribution plate has formed therein a multitude of distribution holes so that the air-fuel mixture can be ejected through the distribution holes and the porous body. The porous body is constituted by nonwoven fabric made by laminating metal fibers in a form of felt. A front surface of the nonwoven fabric is covered by a meshed sheet made of metal, the front surface being defined as the surface on a downstream side as seen in the direction of flow of the air-fuel mixture.

According to this invention, since the porous body is made of nonwoven fabric of metal fibers, the ultrafine metal fibers that are required in knitted textile fabric are not required and, therefore, the cost of the porous body can be reduced. Then, even considering the fact that the meshed sheet is additionally required, the cost can still be made lower than the example in the related art. By the way, the nonwoven fabric alone will be subject to fraying of the metal fibers during use, thereby giving rise to dropping of the metal fibers out of position. On the other hand, by covering the front surface of the nonwoven fabric by the meshed sheet made of metal as in this invention, the metal fibers can be prevented from getting dropped out of the nonwoven fabric.

By the way, it is known to provide the distribution plate with band-shaped hole-free portions in which distribution holes are not formed so that the air-fuel mixture ejected from the combustion plate part is re-circulated in regions corresponding to the hole-free portions, thereby improving the stability in combustion. However, once the nonwoven fabric exceeds 5 mm in thickness, the air-fuel mixture will be dispersed inside the nonwoven fabric and, accordingly, a large amount of air-fuel mixture comes to be ejected also from the region corresponding to the hole-free portions. As a result, the air-fuel mixture can no longer be well re-circulated in the regions corresponding to the hole-free portions. On the other hand, once the nonwoven fabric becomes less than 1 mm in thickness, the flow resistance in the regions corresponding to the distribution holes becomes too small. As a result, flame holding (or flame stabilizing) corresponding to the hole-free portions can no longer be secured, thereby giving rise to the occurrence of flame lifting. Therefore, the thickness of the nonwoven fabric shall preferably be made to be 1 to 5 mm.

Further, at the time of low-load combustion, the air-fuel mixture will be combusted in the neighborhood of the meshed sheet, and the meshed sheet will consequently become red hot. In case the meshed sheet is constituted by a metal net made by knitting a single metal wire into a mesh, the meshed sheet will be thermally expanded by the red heat at the time of low-load combustion. Consequently, the meshed sheet will be floated off from the surface of the nonwoven fabric. As a result, combustion of the air-fuel mixture will take place in the clearance between the rear side of the meshed sheet and the nonwoven fabric, resulting in poor durability. Therefore, the meshed sheet shall preferably be made by knitting a wire member into the form of a mesh, the wire member being formed by bundling together a plurality of metal fibers. According to this arrangement, since the wire member to be formed by bundling together metal fibers is flexible, the thermal expansion by the red heat will be absorbed by the deflection of the wire member. The meshed sheet can thus be prevented from getting floated off from the surface of the woven fabric.

Further, in this invention, the mesh size of the meshed sheet shall preferably be below a flame-out distance of the air-fuel mixture to be ejected out of the combustion plate part. According to this arrangement, even if the meshed sheet should get floated off from the surface of the nonwoven fabric, the flame will not be pulled into the clearance between the rear side of the meshed sheet and the nonwoven fabric. Therefore, the durability can be prevented from getting worse due to the combustion of the air-fuel mixture in this clearance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a combustion apparatus equipped with a totally aerated combustion burner according to an embodiment of this invention.

FIG. 2 is a perspective view of the combustion apparatus as viewed from a side opposite to that in FIG. 1.

FIG. 3 is a sectional view cut away along the line III-III in FIG. 1.

FIG. 4 is a sectional view cut away along the line IV-IV in FIG. 3.

FIG. 5 is a perspective view in an exploded state of the totally aerated combustion burner according to the embodiment.

FIG. 6 is a sectional view of an essential portion in an assembled state of the combustion plate part in FIG. 5.

FIG. 7 is an enlarged view of a part of the meshed sheet to be used in the combustion plate part of the totally aerated combustion burner according to the embodiment.

PREFERRED EMBODIMENTS FOR CARRYING OUT THE INVENTION

A combustion apparatus shown in FIGS. 1 through 4 is provided with: a totally aerated combustion burner 1 having a burner body 11 which is supplied inside thereof with air-fuel mixture (mixture gas of fuel gas and primary air), and a combustion plate part 12 which covers a downward open surface 111 of the burner body 11; and a combustion box 2 having a box flange part 22 at an upper end thereof which is fastened with screws 21 to the body flange part 112 enclosing the open surface of the burner body 11. The combustion box 2 has housed therein a heat exchanger 3 for hot water supply.

The heat exchanger 3 is constituted by a fin-tube type of heat exchanger provided with a multiplicity of fins 31 and a plurality of heat-absorbing tubes 32 which penetrate these fins 31. On an outside surface of side plates 23, 24 on laterally one side and the opposite side of the combustion box 2, there are connected a plurality of connection covers 33 which define connection passages of the adjacent two heat absorbing tubes 32, 32 between each of the side plates 23, 24. In this manner, all the heat-absorbing tubes 32 are connected together in series with one another. Further, the connection covers 33 which define connection passages between the side plates 24 of the laterally opposite side are provided with a water inlet 34, the connection passages being connected to the heat absorbing tubes 32 on an upstream end of the heat exchanger 3.

Furthermore, on an inside of the rear-side side plate 25 of the combustion box 2, the inside being above the heat exchanger 3, there are disposed vertically arranged three pieces of first water passages 5 ₁ made up of tubes. Also on an inside of the front-side side plate 26 of the combustion box 2, the inside being above the heat exchanger 3, there are disposed vertically arranged three pieces of third water passages 5 ₃ made up of tubes. In addition, on an outer surface of the laterally one-side side plate 23 of the combustion box 2, there are connected: an inlet-side header cover 51 which defines a connection passage which connects the vertically disposed three pieces of first water passages 5 ₁ to the heat absorbing tube 32 on a downstream end of the heat exchanger 3, between the laterally one-side side plate 23; and an outlet-side header cover 52 which defines, between the side plate 23, a connection passage which connects the vertically disposed three pieces of third water passages 5 ₃, the outlet-side header cover 52 being provided with a hot water outlet 53. Furthermore, as shown in FIGS. 2 and 3, the laterally opposite side of the side plate 24 of the combustion box 2 is provided with second water passages 5 ₂ which connect the rear-side first water passages 5 ₁ and the front-side water passages 5 ₃. Each of the second water passages 5 ₂ is made up of: a laterally inward dent which is formed in the side plate 24; and a cover 54 which is mounted on an outer surface of the side plate 24 in a manner to cover the dent. It is thus so arranged that the water to be supplied from the water inlet 34 is heated by the heat exchanger 3, and the heated water flows out of the hot water outlet 53 through the connection passage inside the inlet-side header cover 51, the first water passages 5 ₁, the second water passages 5 ₂, and the third water passages 5 ₃, and the connection passage inside the outlet-side header cover 52. In addition, the laterally one-side side plate 23 of the combustion box 2 is provided with a fourth water passage 5 ₄ which extends rearward from an upper portion of the connection passage inside the outlet-side header cover 52, the fourth water passage 5 ₄ being constituted by: a laterally inward dent which is formed in the side plate 23; and a cover 52 a which covers this dent and which is integral with the outlet-side header cover 52. It is thus so arranged that each of the side plates 23-26 of the combustion box 2 is cooled by the water which flows through these first through fourth water passages 5 ₁-5 ₄.

Further, the front-side side plate 26 of the combustion box 2 has mounted thereon electrode parts 6 which are protruded through the side plate portion between the two, i.e., the first and the second from the top, of the third water passages 5 ₃, 5 ₃, the electrode parts 6 inclusive of an ignition electrode 61, a grounding electrode 62, and a flame rod 63. The electrode parts 6 are additionally provided with an inspection window 64 through which the inside of the combustion box 2 can be visually inspected.

Next, detailed explanation will now be made of the totally aerated combustion burner 1. The burner body 11 has opened therethrough an inlet port 113 for connecting thereto a fan 4 which supplies air-fuel mixture. The inlet port 113 has mounted thereon a check valve 13 which prevents the air-fuel mixture remaining inside the burner body 11 from flowing backward to the side of the fan 4. The check valve 13 is constituted by: a resin-made valve box 131 which is built into the inlet port 113; and a resin-made valve plate 132 which is rotatably mounted, so as to be opened or closed, in the opening of the valve box 131 which looks inward of the burner body 11.

With reference also to FIGS. 5 and 6, the combustion plate part 12 has: a burner frame121 in the shape of a picture frame; a porous body 123 which is made of metal fabrics disposed in a manner to cover, from the burner-body side (upward), an opening 122 enclosed by the burner frame 121; and a distribution plate 124 which is disposed in an overlapped manner on a back surface (upper surface) of the porous body 123, the back surface being defined as the surface on an upstream side as seen in the direction of flow of the air-fuel mixture, the distribution plate 124 having formed therein a multitude of distribution holes 124 a. In this arrangement, the air-fuel mixture supplied into the burner body 11 is ejected, through the distribution holes 124 a and the porous body 123, out of the opening 122, thereby performing totally aerated combustion (combustion requiring no secondary air). The opening 122 is curved into an arcuate shape in cross section in the front-to-back direction. Similarly, the porous body 123 and the distribution plate 124 are also curved into an arcuate shape in cross section in the front-to-back direction.

The burner frame 121 has: an opening peripheral part 121 a that is positioned on the same plane as the opening 122; a side-plate part 121 b which is bent from the opening peripheral part 121 a to the burner-body 11 side (i.e., upward); and a frame flange part 121 c which protrudes outward from an upper end of the side-plate part 121 b. Then, the frame flange part 121 c is sandwiched between the body flange part 112 and the box flange part 22 and, further, a packing 7 is interposed between the frame flange part 121 c and the body flange part 112, thereby securing sealing properties. In addition, insulation material 8 is fitted on the lower surface of the frame flange part 121 c.

The porous body 123 is constituted by nonwoven fabric in which metal fibers, e.g., of heat-resistant steel and the like are laminated in the form of felt. The front surface (lower surface) of this nonwoven fabric 123 is covered by a meshed sheet 125 of metal make, the front surface of the nonwoven fabric 123 being defined as the downstream side as seen in the flow of the air-fuel mixture. The diameters of the metal fibers which constitute the nonwoven fabric 123 may be about 35-100 μm. Therefore, there will be required no ultrafine metal fibers that are required in the above-mentioned related art in which the porous body is constituted by woven fabric formed by knitting metal fibers into a knit. The cost of the porous body 123 can thus be reduced. Even considering the fact that the meshed sheet 125 is additionally required in this invention, the cost of this invention can still be made lower than that of the related art. Further, in the case of nonwoven fabric 123 alone, the metal fibers will be frayed and dropped out of position in the course of use. However, by covering the surface of the nonwoven fabric 123 with the meshed sheet 125 as in this embodiment, the metal fibers can be prevented from dropping out of position from the nonwoven fabric 123.

By the way, in assembling the combustion plate part 12, in order to increase the adhesion properties between the nonwoven fabric 123 and the meshed sheet 125, compression is made first in a state in which the meshed sheet 125 is overlapped on the front surface of the nonwoven fabric 123. Thereafter, in a state in which the distribution plate 124 is overlapped on the back surface (upper surface) of the nonwoven fabric 123, the peripheral part of the above-mentioned thus obtained semi-product is spot-welded to the opening peripheral part 121 a of the burner frame 121 at predetermined circumferential spacing.

As shown in dashed line in FIG. 5, the distribution plate 124 is provided with hole-free portions (portions having no hole) 124 b in a band shape, for example, in a band shape of a lattice pattern in which the hole-free portions cross lengthwise and breadthwise. According to this arrangement, the air-fuel mixture to be ejected from the combustion plate part 12 is recycled in a region corresponding to the hole-free portions 124 b, thereby improving the stability in combustion. However, once the nonwoven fabric 123 exceeds 5 mm in thickness, the air-fuel mixture comes to be dispersed inside the nonwoven fabric 123 and, consequently, the air-fuel mixture comes to be ejected in a large amount out of the region corresponding to the hole-free portions 124 b. As a result, the air-fuel mixture will no longer be recycled well in the region corresponding to the hole-free portions 124 b. Further, once the nonwoven fabric 123 falls below 1 mm in thickness, the ventilation resistance will become too small in the region corresponding to the distribution holes 124 a. As a result, flame holding can no longer be secured in a region corresponding to the hole-free portions 124 b, giving rise to frequent occurrence of flame lifting. Therefore, the thickness of the nonwoven fabric 123 shall preferably be made to be 1-5 mm.

Further, at the time of low-load combustion, the air-fuel mixture will be combusted in the vicinity of the meshed sheet 125, and the meshed sheet 125 will become red hot. In case the meshed sheet 125 is constituted by a metal net which is made by knitting a single metal wire into a mesh, the meshed sheet 125 will be thermally expanded by the red heat at the time of low-load combustion, and the meshed sheet 125 will be floated off from the surface of the nonwoven fabric 123. As a result, the air-fuel mixture will be combusted in the clearance between the nonwoven fabric 123 on the rear side of the meshed sheet 125 and the nonwoven fabric 123, thereby impairing the durability.

As a solution, in this embodiment, as shown in FIG. 7, the meshed sheet 125 is arranged by knitting, into a mesh, a wire member (bundled wire) 125 b formed by bundling together a plurality of metal fibers 125 a (about 100 μm in diameter) of heat-resisting steel and the like. According to this arrangement, since the wire member (bundled wire) 125 b formed by bundling metal fibers 125 a together is flexible, the thermal expansion by red heat will be absorbed by the deflection of the bundled wire 125 b. Therefore, the meshed sheet 125 can be prevented from getting floated off from the surface of the nonwoven fabric 123.

In addition, according to this embodiment, the mesh size (maximum width of a stitch) W of the meshed sheet 125 is arranged to be below the flame-out distance of the air-fuel mixture to be ejected out of the combustion plate part 12. For example, in case the kind of the fuel gas is, e.g., 13A, and the excess air ratio of 1.3 is ejected, the flame-out distance is 2 mm. The mesh size W shall therefore be made below 2 mm. According to this arrangement, even though the meshed sheet 125 may possibly be floated off from the surface of the nonwoven fabric 123, there is no possibility of the flame getting sucked into the clearance between the rear side of the meshed sheet 125 and the nonwoven fabric 123. The durability can thus be prevented from getting worse due to the combustion of the air-fuel mixture in this clearance.

Descriptions have so far been made of an embodiment of this invention with reference to the drawings, but this invention shall not be limited thereto. For example, the totally aerated combustion burner of the above-mentioned embodiment is disposed such that the open surface 111 of the burner body 11 looks downward. This invention can, however, be applicable to a totally aerated combustion burner in which the open surface 111 of the burner body 11 looks upward. Furthermore, in the above-mentioned embodiment, the porous body l23 is disposed in a manner to cover the opening 122 of the burner frame 121. However, this invention can also be applied to a totally aerated combustion burner which is arranged that the porous body and the distribution plate are made cylindrical, and that the air-fuel mixture supplied to this cylindrical inner space is ejected outward through the distribution holes of the distribution plate and the porous body.

EXPLANATION OF MARKS  1 totally aerated combustion burner  12 combustion plate part 123 porous body; nonwoven fabric 124 distribution plate 124a distribution hole 124b hole-free portion (portion having no hole) 125 meshed sheet (net-like sheet) 125a metal fiber 125b wire member (bundled wire) 

What is claimed is:
 1. A totally aerated combustion burner comprising a combustion plate part through which air-fuel mixture is ejected, the combustion plate part including: a porous body made of metal fibers; and a distribution plate stacked on a back surface of the porous body, the back surface being defined as an upstream-side surface as seen in a direction of flow of the air-fuel mixture, the distribution plate having formed therein a multitude of distribution holes so that the air-fuel mixture can be ejected through the distribution holes and the porous body, the porous body being constituted by nonwoven fabric made by laminating metal fibers in a form of felt, a front surface of the nonwoven fabric being covered by a meshed sheet made of metal, the front surface being defined as the surface on a downstream side as seen in the direction of flow of the air-fuel mixture.
 2. The totally aerated combustion burner according to claim 1, wherein the distribution plate includes a band-shaped hole-free portion having formed therein no distribution hole, and wherein the felt has a thickness of 1-5 mm.
 3. The totally aerated combustion burner according to claim 1, wherein the meshed sheet is made by knitting a wire member into a form of a mesh, the wire member being formed by bundling together a plurality of metal fibers.
 4. The totally aerated combustion burner according to claim 1, wherein the mesh size of the meshed sheet is below a flame-out distance of the air-fuel mixture to be ejected out of the combustion plate part. 